The present invention broadly relates to wrought aluminum alloy of the "super pure" or "pure" grade which range in composition from a minimum of 99.00% aluminum (alloy 1100) to a maximum of 99.99% aluminum (alloy 1199) and thus contain no major alloying element. For a more detailed description of such alloys and their designations and properties, reference may be had to the text, ALUMINUM, Volume 1, pages 303 through 313 by American Society of Metals 1967, edited by Kent R. VanHorn which is hereby incorporated by reference into this application. While in one commercial preferred application, the invention is directed to 1145 aluminum alloy (99.45% aluminum), commonly used for producing aluminum foil, the invention may also be applicable to other pure or super pure grade alloys described above.
It is an established fact that pure aluminum alloy such as 1145 alloy as conventionally produced through continuous casting in strip form is generally harder and thus less ductile and more difficult to recrystallize during annealing following cold working than the same alloy made by the more conventional "direct-chill" casting method. Aluminum alloy ingots produced by the direct chill casting method are typically cast in heavy sections, hot rolled and then subjected to various cold rolling and annealing cycles until the desired final gauge is reached. This process has been satisfactorily applied in the commercial production of aluminum foil from pure grade aluminum alloy. However in contrast, commercial production of the same foil from the same pure grade alloy through use of a continuous strip casting method utilizing the same cold working and annealing procedures has been found to be more difficult due to the hardness and recrystallization problems mentioned above. As a result, the wrought product must be subjected to additional cold working and annealing and also at times at higher annealing temperatures when compared to a product of the direct chill casting process.